Energetics of Lithium-Ion Battery Failure during Use and Thermal Abuse

Calcagno, William

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Energetics of Lithium-Ion Battery Failure during Use and Thermal Abuse

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This research tested the impact of the usage condition of lithium-ion batteries on their thermal runaway properties during thermal abuse in a modified copper slug calorimeter. Two chemistries of cylindrical 18650 lithium-ion cells were used: LiNiMnCoO2 (NMC) and LiNixCoyAl1-x-yO2 (NCA). During each test, 20±0.2 watts were used to heat the cell. During each test, discharge was simulated by a series of resistors connected to the top and bottom electrical contacts of the battery. It was found that the average time to thermal runaway for NCA cells decreased as discharge current increased, while the average time to thermal runaway for NMC cells increased if discharge was present but did not increase continuously with increased discharge current. It was also found that the average mass loss for NMC cells decreased as discharge increased, a trend that did not repeat in the NCA cell tests. In addition, it was observed that the NMC cells lost charge faster than the NCA cells, which resulted in NMC cells undergoing thermal runaway during the high-discharge tests at a significantly higher temperature than every other test condition. The spark velocity and duration of thermal runaway trends were similar between both battery types; average and maximum spark velocities decreased as discharge current increased and duration of thermal runaway increased as discharge rate increased except for the high-discharge NMC battery tests. Copper slug calorimetry results also showed the total internal heat generation in NMC battery tests increased as discharge current increased until the high-discharge tests, at which point the total internal heat generation dropped. NCA battery tests showed almost the opposite trend, where total internal heat generation values decreased as discharge rate increased until the high-discharge test condition where they increased. Peak internal heat generation values showed the same general trend between battery types, where they decreased as discharge rate increased. These results suggest that while this test methodology can be generalized and applied to different battery chemistries, the impact of a lithium-ion battery’s usage condition (i.e., discharge current) on its thermal runaway properties cannot be generalized between different chemistries and each new chemistry should be tested in the future.

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